To say nothing of various electronic devices, secondary cells are used as power supplies for automobiles and backup. A lithium-ion secondary cell using the doping and de-doping of lithium ions is widely known as one of the secondary cells. The lithium-ion secondary cell may change in properties due to the use environment and the use time. Hence, various proposals have been made for detecting the state of a lithium-ion secondary cell. For example, the following Patent Document 1 describes a technology for using the ratio of the amount of a change in the voltage of the lithium-ion secondary cell to a change in the electric storage amount of the lithium-ion secondary cell (dV/dQ) to determine the presence or absence of a deterioration of the lithium-ion secondary cell.